Cobalt chromium based alloy

ABSTRACT

A cobalt/chromium based alloy suitable for use in making dental prostheses and surgical implants, and also for use in making machine parts which are subject to severe corrosive conditions and mechanical loads at high temperatures, comprises by weight, 26 percent to 31 percent chromium, from 4 percent to 6.5 percent molybdenum, up to 2 percent silicon, up to 6 percent maganese, up to 1 percent iron, up to 0.5 percent boron, up to 0.5 percent carbon, from 0.15 percent to 0.5 percent nitrogen, and the remainder cobalt except for impurities, the sum of the carbon and nitrogen contents not exceeding 0.7 percent.

United States Patent Rademacher Feb. 11, 1975 [54] COBALT CHROMIUM BASED ALLOY 2,381,459 8/1945 Merrick 75/171 3,606,615 9 I97] R d' t l. 75 HI Invent: Rademacher, w'tten'Heven 3,758,299 9i1973 Eh nis e t ..75i171 Germany [73] Assignee: Edelstahlwerk Witten Prim ry ExaminerR. Dean Aktiengesellschaft, Witten, Germany A rn y, Ag n or Fi -T wn, M eady and 221 Filed: May 22, 1973 Stanger [21] Appl. No.: 362,867 [57] ABSTRACT A cobalt/chromium based alloy suitable for use in [30] Foreign Application Priority Data making dental prostheses and surgical implants, and May 26, 1972 Germany 2225577 for in making machine Parts which are subject to severe corrosive conditions and mechanical loads at 52] us. c1 75/171, 3/1, 32/2, high temperatures, comprises by Weight 26 Percent to 32/10 A 31 percent chromium, from 4 percent to 6.5 percent 51 1m. 01 C22c 19/00 molybdenum "P to 2 Permt Silicon, "P to 6 P 581 Field of Search 75/171, 170; 148/32, 32.5; maganese "P 1 Percem P 05 Percent 3/1; 32/], 2 10 A ron, up to 0.5 percent carbon, from 0.15 percent to 0.5 percent nitrogen, and the remainder cobalt except [56] References Cited for impurities, the sum of the carbon and nitrogen contents not exceeding 0.7 percent.

10 Claims, No Drawings 1 COBALT ,CHROMIUM BASED ALLOY This invention relates to cobalt/chromium based alloys suitable for use in making dental prostheses structures and surgical implants.

Cobalt/chromium alloys are used in machinery construction predominantly for making components which are subjected to severe corrosive conditions and me chanical loadings at high temperatures. They are however equally well known in surgery for the making of implants and in dentistry for making prosthetic struc tures.

In these medical fields, alloys which, in addition to cobalt as the basic element, also contain by weight from 26 percent to 31 percent chromium, from 4 percent to 6.5 percent molybdenum, up to 1 percent each of silicon, manganese and iron, and from 0.3 percent to 0.5 percent carbon, are of particular importance. In addition, alloys are also used which, principally owing to the cost of cobalt content, contain instead up to 20 percent nickel. These may also have the silicon and manganese contents raised up to 6 percent, and may also be provided with additions of copper, aluminium, titanium, niobium, vanadium, zirconium, tantalum, beryllium and boron, either individually or in combination.

The use of these alloys in surgery and dentistry is based upon the fact that they are resistant to the corrosive conditions existing in the body and in the oral cavity; are easy to cast to the frequently very complicated shapes required; are easy to work, and possess a high modulus of elasticity and high strength and hardness. The published values are: for the modulus of elasticity an average of 220,000 N/mm and depending upon the strength of the alloy, .for the technical elastic limit (0.01 limit) approximately 390 and 440 N/mm respectively, for the 0.2-limit approximately 600 and 625 N/mm respectively, and for the tensile strength approximately 880 and 910 N/mm respectively. Values for the hardness are 340 and 380 Brinell hardness respectively.

A disadvantage of these cobalt/chromium alloys is their low capacity for deformation, that is low ductility. This is usually expressed by the elongation at rupture. The published values vary considerably but are predominantly in a range from 2 percent to 6 percent. The highest value published is 8 percent. Because of these low elongation values for the alloys, severe limits are set on the plastic deformations which can be applied to articles made from them, for example straightening operations on the holding braces of dental prosthetic structures, if the risk of breakage is to be avoided.

For this reason, titanium-containing alloys with a cobalt base having improved capacity for deformation for the same or an increased strength have been developed. These alloys contain, by weight, in addition to cobalt, from percent to percent chromium, from 5 percent to percent nickel, up to 3 percent molybdenum, up to 1 percent carbon, silicon, manganese, aluminium and/or iron and from 4 percent to 10 percent titanium. The published values of their elastic limit range, for the 0.2-limit from approximately 560 to 800 N/mm for the tensile strength from approximately 845 to 1,110 N/mm for the elongation from 10 to 12.7 percent and for the Brinell hardness from 330 to 380 kp/mm Due to the very high affinity of titanium for oxygen, these alloys suffer from the substantial disadvantage that they must be melted under vacuum or under a protective gas, and that, when manufacturing prostheses and implants, they can be melted only by using an acetylene-oxygen-burner with a flame adjusted absolutely to neutral, and not by the high frequency induction heat sources which are also frequently used.

Finally, alloys having a cobalt/chromium base are also known which, in addition to cobalt, contain, by

weight, from 20 percent to 28 percent chromium, from 10 percent to 20 percent nickel, from 3.7 percent to 4.1 percent molybdenum, and from 0.18 percent to 0.22 percent carbon. As a result of this narrow limitation of the molybdenum and carbon contents, the e1ongation is raised to from 10 percent to 14.5 percent. This advantage is however offset by the substantial disadvantage of an appreciable drop in the elastic limit. The values published are, for the 0.l-limit from 375 to 415 N/mm for the tensile strength from 595 to 715 N/mm and for the Diamond Pyramid hardness from 270 to 310 kp/mm It is the object of this invention to provide an alloy which avoids the disadvantages mentioned above while at the same time exhibiting an adequate or even an improved ductility.

To this end, according to this invention, an alloy comprises, by weight, from 26 percent to 31 percent chromium, from 4 percent to 6.5 percent molybdenum, up to 2 percent, and preferably only up to 1.5 percent silicon, up to 6 percent and preferably only up to 3 percent manganese, up to 1 percent iron, up to 0.5 percent boron, up to 0.5 percent carbon and from 0.15 percent to 0.5 percent nitrogen the remainder cobalt except for impurities, and the sum of the carbon and nitrogen contents not exceeding 0.7 percent The nitrogen content is preferably from 0.20 percent to 0.35 percent, or advantageously up to a maximum of only 0.30 percent.

For some applications, both the silicon and the manganese contents should not exceed 1 percent each. A boron content of preferably from 0.01 percent to 0.15 percent, is advantageous.

Examples of alloys in accordance with the invention are set out in Table 1. Table 11 gives the associated mechanical properties.

Table I Chemical Composition (/0 by Weight) Example C N (C N) Si Mn Co Cr Mo B 3. Table ll Mechanical Properties 0.2- Tensile Elongation Hardness Elastic Strength HV 30 Example limit (Nlmm (N/mm") (7:) (kg/mm) 1 580 735 8.2 3 l6 2 565 795 l4.6 31 l 3 570 845 l7.l 308 4 675 lOOO I20 327 5 685 1005 12.0 316 6 655 960 8.3 326 7 655 940 10.9 332 8 635 895 7.1 339 9 725 1010 8.2 328 .ness is nevertheless somewhat reduced. This suggests that the increase in the tensile strength values in the tensile test is a direct result of the improved deformability. From a comparison of Examples 7 and 9 with Example 8, it is apparent that in the total content of carbon and nitrogen, the carbon should preferably constitute the smaller component and should preferably not exceed approximately 0.2 percent.

In Examples 4 to 6 and 9, the manganese content has been raised to approximately 3 percent, in order to increase the dissolving capacity of the alloys for nitrogen. An addition of boron improves the capacity for casting (Examples 5 and 6). The mechanical properties are not in any way thereby adversely affected.

I claim:

1. An alloy consisting essentially of from 26 percent to 3l percent chromium, from 4 percent to 6.5 percent molybdenum, up'to 2 percent silicon, up to 6 percent manganese, up to 1 percent iron, up to 0.5 percent boron, up to 0.5 percent carbon, from 0. [5 percent to 0.5 percent nitrogen, with the ,balance being cobalt and impurities, the sum of said carbon content and said nitrogen content not exceeding 0.7 percent.

2. An alloy as claimed in claim 1, wherein said silicon content is no more than 1.5 percent.

3. An alloy as claimed in claim 1, wherein said manganese content is no more than 3 percent.

4. An alloy as claimed in claim 1, wherein said nitrogen content is from 0.2 percent to 0.35 percent.

5. An alloy as claimed in claim 1, wherein said carbon content is no more than 0.2 percent.

6. An alloy as claimed in claim 1, wherein said silicon content and said maganese content are each no more than 1 percent.

7. An alloy as claimed in claim 1, wherein said boron content is from 0.01 percent to 0.15 percent.

8. A dental prosthesis made from an alloy as claimed in claim 1.

9. A surgical implant made from an alloy as claimed in claim 1.

10. A machine component made from an alloy as claimed in claim 1. 

1. AN ALLOY CONSISTING ESSENTIALLY OF FROM 26 PERCENT TO 31 PERCENT CHROMIUM, FROM 4 PERCENT TO 6.5 PERCENT MOLYBDENUM, UP TO 2 PERCENT SILICON, UP TO 6 PERCENT MANGANESE, UP TO 1 PERCENT IRON, UP TO 0.5 PERCENT BORON, UP TO 0.5 PERCENT CARBON, FROM 0.15 PERCENT TO 0.5 PERCENT NITROGEN, WITH THE BALANCE BEING COBALT AND IMPURITIES, THE SUM OF SAID CARBON CONTENT AND SAID NITROGEN CONTENT NOT EXCEEDING 0.7 PERCENT.
 2. An alloy as claimed in claim 1, wherein said silicon content is no more than 1.5 percent.
 3. An alloy as claimed in claim 1, wherein said manganese content is no more than 3 percent.
 4. An alloy as claimed in claim 1, wherein said nitrogen content is from 0.2 percent to 0.35 percent.
 5. An alloy as claimed in claim 1, wherein said carbon content is no more than 0.2 percent.
 6. An alloy as claimed in claim 1, wherein said silicon content and said maganese content are each no more than 1 percent.
 7. An alloy as claimed in claim 1, wherein said boron content is from 0.01 percent to 0.15 percent.
 8. A dental prosthesis made from an alloy as claimed in claim
 1. 9. A surgical implant made from an alloy as claimed in claim
 1. 10. A machine component made from an alloy as claimed in claim 